RDFa is a method for embedding Rich Data Formats metadata within HTML documents. It allows metadata like titles, descriptions and URLs to be added to HTML pages in a way that is readable both by humans and machines. The summary describes how RDFa works by defining resources with URIs and properties, and how this extracted data can be distilled and validated using various RDFa tools on the W3C website.

1. How RDFa works

2. How does RDFa work
Session 2/4

3. An RDFa basics tutorial by Manu Sporny
http://www.youtube.com/watch?v=ldl0m-5zLz4&feature=player_embedded

4. Real metadata
Resource description framework
‣ RDF is a generic "way" of using definitive metadata with web resources.
‣ RDF describes "things" (entities, defined by uniform resource identifiers,
URIs) by assigning properties and corresponding values—statements are
known as "triples" consisting of [subject] [predicate] [object].
‣ The predicate URI usually references a term in a standard metadata
vocabulary, resulting in unambiguous meaning.
‣ Any part of the triple can be a URI and URIs can point to other URIs that can
be read using HTTP and extended (or related) in other web resources, thus a
scalable model and very flexible.
http://www.w3.org/TR/rdf-primer/ http://www.w3.org/RDF/

5. RDFa distiller
Extract RDF from HTML + RDFa
W3C service to identify and list RDF from a web page
‣ using web address, local file or direct text inputs
‣ provides “clean” view of data hierarchy
‣ enables simple check on markup validation *and* intended meaning
http://www.w3.org/2007/08/pyRdfa/

6. Distilled RDFa page
<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
xmlns:v="http://rdf.data-vocabulary.org/#"
xmlns:xhv="http://www.w3.org/1999/xhtml/vocab#"
xmlns:xml="http://www.w3.org/XML/1998/namespace"
>
<v:Person>
<v:nickname>mungeo</v:nickname>
<v:address>
<v:Address>
<v:region>Ulster</v:region>
<v:locality>Donegal</v:locality>
</v:Address>
</v:address>
<v:url rdf:resource="http://www.platypusconsultancy.com"/>
<v:name>George Munroe</v:name>
<v:title>consultant trainer</v:title>
<v:affiliation>Netskills</v:affiliation>
</v:Person>
</rdf:RDF>
RDFa

7. Validating the RDF extracted from an RDFa
file and exploring the data structure
‣ obtain a tabular description of entity classes and corresponding properties
‣ list inherent RDF triples
‣ visualise relationships with simple graphical representations
http://www.w3.org/RDF/Validator/

8. View RDF triples within RDF file
RDFa

9. View graph of entities and properties
RDFa

10. Practical exercise
Extracting RDF from RDFa
‣ open the W3C RDFa distiller service with your web browser
‣ use the “Distill by file upload” option, select your sample RDFa file and “Go!”
‣ view the page source of the output file and note the RDF tagging
‣ copy all of the page source of the output file (RDF)
‣ open the W3C RDF validation service with your web browser
‣ use the “Check by direct input” option and paste in your RDF source
‣ select “Triples and graph” from the “Display result options” section
‣ click the “Parse RDF” button and explore the RDF triples and graph produced
by selecting “Grid view” and “SVG graph”
‣ if time permits repeat the above process with the W3C RDF primer sample
file (http://www.w3.org/2006/07/SWD/RDFa/primer/alice-example.html)
only use the validator directly by selecting the “Check by URI” option and
supplying the distiller service address with the sample RDFa file in a query
string as follows:
http://www.w3.org/2007/08/pyRdfa/extract?uri=http://www.w3.org/2006/07/SWD/
RDFa/primer/alice-example.html

11. Metadata vocabularies
The importance of shared metadata
Everyone (and every computer) must have a common understanding
of what particular entities and properties actually are
‣ concept of XML namespaces, used to make descriptions of entity classes and
corresponding properties available via the web
‣ these descriptions supplied as RDF (or RDFa) files with a URL (URI)
And there’s more to it than just a flat list of entities and properties
‣ a real understanding involves being aware of the relationships between
entity classes as well as what properties are associated with an entity
‣ possibly a very complex “ontology” but built very simply from triples where
the object of one triple may be the subject of another
RDFa

12. Namespaces
These namespaces are used to describe
entities in X number of documents
Namespaces (819 known namespaces) Number of documents
http://xmlns.com/foaf/0.1/ 1,261,416
http://purl.org/goodrelations/v1# 645,210
http://blogs.yandex.ru/schema/foaf/ 584,781
http://www.w3.org/2002/07/owl# 451,113
http://sites.wiwiss.fu-berlin.de/suhl/bi... 252,361
http://rdfs.org/sioc/ns# 183,228
http://www.w3.org/2003/01/geo/wgs84_pos# 157,659
http://rdfs.org/sioc/types# 117,621
http://semantic-mediawiki.org/swivt/1.0# 64,281
http://xmlns.com/foaf/spec/ 50,514
http://pingthesemanticweb.com/

13. Entities
The number of each entity type known by
pingthesemanticweb.com
Entity types (10,500 known entity types) Count
http://xmlns.com/foaf/0.1/Person 19,015,352
http://xmlns.com/foaf/0.1/Document 5,115,311
http://purl.org/goodrelations/v1#Product... 1,418,899
http://purl.org/goodrelations/v1#UnitPri... 999,893
http://purl.org/goodrelations/v1#Busines... 753,812
http://purl.org/goodrelations/v1#Offerin... 644,652
http://purl.org/goodrelations/v1#TypeAnd... 626,684
http://blogs.yandex.ru/schema/foaf/Posts 585,188
http://www.w3.org/2002/07/owl#Ontology 446,664
http://purl.org/goodrelations/v1#Product... 374,456
http://pingthesemanticweb.com/

14. Exploring vocabularies
Commonly used metadata vocabularies
Google (person, organisation, review, event, recipe)
‣ http://rdf.data-vocabulary.org/
FOAF (Friend Of A Friend)
‣ http://xmlns.com/foaf/0.1/
GoodRelations (ecommerce)
‣ http://www.heppnetz.de/ontologies/goodrelations/v1.owl
Dublin Core (generic document)
‣ http://dublincore.org/2008/01/14/dcelements.rdf
Creative Commons (licensing)
‣ http://creativecommons.org/ns
SKOS (Simple Knowledge Organisation System)
‣ http://www.w3.org/2009/08/skos-reference/skos.rdf
RDFa

15. Viewing complex vocabularies—ontologies
Use the OpenLink Data Explorer extension in Firefox
http://ode.openlinksw.com/

22. Exploring vocabularies
Digging into metadata vocabularies
Use the Firefox browser with OpenLink Data Explorer extension and/
or W3C RDF validator and grapher online service to view the following
vocabularies:
‣ Dublin Core at: http://dublincore.org/2008/01/14/dcelements.rdf
‣ GoodRelations at: http://www.heppnetz.de/ontologies/goodrelations/v1.owl
Use the pyRdfa distiller service to extract and view the RDF
vocabulary information from the following descriptions:
‣ FOAF at: http://xmlns.com/foaf/0.1/
‣ Creative Commons at: http://creativecommons.org/ns

23. RDFa tools
Summary of useful RDFa related tools
RDFa distiller (extract pure RDF from HTML + RDFa)
‣ http://www.w3.org/2007/08/pyRdfa/
‣ get RDF directly from http://example.com/sample.html using single address
http://www.w3.org/2007/08/pyRdfa/extract?uri=http://example.com/sample.html
RDF validator and grapher
‣ http://www.w3.org/RDF/Validator/
OpenLink Data Explorer extension for Firefox
‣ https://addons.mozilla.org/en-US/firefox/addon/8062
List global namespaces and entities
‣ http://pingthesemanticweb.com/
RDFa